This invention relates to an improved process for preparing fiberboard having heat resistance and improved releasability and to the treated fiberboard thus produced. Fiberboards (sometimes called pressboards or hardboards) are boards manufactured from cellulosic fibers interfelted, preferably with a binding material, to produce an initial adhesive bond among the fibers. In a typical procedure, the wet interfelted panels are shaped and cut to the approximate desired dimensions (ordinarily to form a semi-hard board) and transferred to a drying and baking oven wherein the remaining moisture is evaporated and the boards are baked to set the binders therein. To allow the fiber panel to be released from the platen and the press for subsequent compression to size, the panel is treated prior to drying and compression with a thermoset resin blend. An additional treatment of the basic board for water resistance (tempering) is often carried out with various combinations of polymeric materials and drying oils. Thus, the compressed, hot board may be immersed in a bath of a siccative material such as a drying oil or drying oil blend of oxidized resins so that the surface and edges of the board are impregnated with up to 6% of the oil. The treating oil may also be applied by spraying or roll coating. The impregnated board is then baked at high temperature to oxidize (polymerize) the drying oil to a tough, insoluble form to yield the tempered fiberboard in final form. The fiberboard exhibits greatly improved physical properties such as resistance to moisture, strength, and hardness, possesses paintability and machinability, and is mostly used in applications in which it is likely to be exposed to external conditions of weather or dampness.
U.S. Pat. No. 4,517,240 (issued May 14, 1985 to Arthur A. Tracton et al.) discloses a one-step process for preparing fiberboard wherein the separate applications of hydrocarbon resins for release properties and a drying oil for water-resistance are replaced by a one-step application of an aqueous composition which provides water-resistance and releasability equal to or better than the tempered fiberboard of the prior art. The aqueous treating composition comprises about 3-20% by weight of an acrylic or vinyl acetate emulsion or solution polymer and about 0.05-3.0% by weight of a fluid, water-soluble organosilicone copolymer of dimethylpolysiloxane polyoxyalkylene ether wherein the alkylene moiety is ethylene, propylene or mixtures thereof.
U.S. Pat. No. 4,238,438 (issued Dec. 9, 1980 to Gerald F. Laughinghouse et al.) discloses an improved dry formed method for making hardboard. The coating composition which is applied to the surface fibers of the mat comprises 62-95% water, 4-25% of a hydroxy radical-containing compound having a boiling point of from 100.degree.-316.degree. C. (212.degree.-600.degree. F.) and selected from the group consisting of alcohols and their esters, and from 1-25% polyvinyl acetate. The mat is then pressed for a time and at a temperature and pressure effective to consolidate the fibers and permanently bind them by virtue of the glue system, the glue system having been mixed with the fibers prior to formation of the mat.
Water-soluble starches, e.g., boiled potato or corn starch preferably reacted with 2-5% ethylene oxide or a similar oxide, are used as extenders in barrier coating compositions consisting essentially of a water-soluble, predominantly acrylamide polymer and a hydrophilic-hydrophobic vinyl polymer containing 25-75 mole % of styrene linkages. The coating composition is used on fibrous cellulosic materials such as paper, paperboard, and hardboard such as "Masonite". See U.S. Pat. No. 3,808,161 issued April 30, 1974 to O. M. Lipscomb. The coating, with or without the starch (up to 8 parts by weight of a water-soluble starch per part by weight of the mixture of polymers), improves holdout of the primer.
Various derivatized or converted starches have been used as emulsifers or colloids in vinyl ester polymerizations. For example, oxidized starches from any vegetable source and waxy starches have been used as protective colloids during vinyl acetate emulsion polymerization. The resulting latices are particularly useful as an adhesive for affixing backing pads to carpeting. Other end uses include paper coatings, crease-resistant finishes for textiles, paperboard adhesives, and adhesive bases for paint, and aids in pigment dyeing. See U S. Pat. No. 3,632,535 issued Jan. 4, 1972 to R. E. Gramera et al.
Starch colloids used as stabilizers in aqueous vinyl acetate (co)polymer emulsions include hydroxyalkyl starches (e.g., hydroxyethyl and hydroxypropyl starch) and carboxylated starches (e.g., carboxymethyl starch), and/or methyl- -D-glucoside. The starches stabilize the emulsion, prevent precipitation at elevated temperatures, and in the presence of borax in solution improve the tensile strength of the polymer films. See U.S. Pat. No. 3,769,248 issued Oct. 30, 1973 to L. P. Kovats.
Starch esters and half-esters, preferably those derived from a low molecular weight hydrolyzed starch and/or its derivatives which are reacted with at least about 0.25 mole of at least one cyclic anhydride of a polycarboxylic acid for each anhydroglucose unit are used as dispersants in paints and coatings. Typical esters include the succinate and octenyl succinate. See U.S. Pat. No. 4,061,610 issued December 6, 1977 to R. C. Glowaky. Low molecular weight mixed starch esters, e.g , starch acetate-succinate or propionate-succinate, are also useful as dispersants in aqueous coating compositions comprising polymeric resin binders and pigments. See U.S. Pat. No. 4,061,611 issued December 6, 1977 to R. C. Gloaky et al.
Hydroxypropyl and/or hydroxyethyl starches are used as protective colloids in the preparation of water-containing vinyl acetate (co)polymer dispersions. Emulsifiers are also used in the polymerization. The resulting dispersions are useful as adhesives in the wood and paper industries, in coatings for paper, in the paint industry, and as a reinforcing for book backs. See U.S. 4,322,322 issued March 30, 1982 to P. F. T. Lambrechts et al.
Cyanoalklated, hydroxyalkylated, and carboxyalkylated starches are used as protective colloids in the preparation of aqueous polymer dispersions prepared from vinyl esters and up to 50% by weight of another monomer. The resulting dispersions can be used as adhesives for paper, foil and wood, as paint, as textile or paper fillers, in the construction industry as an adjuvant to hydraulically setting materials, especially stable cement and concrete materials, and particularly for the preparation of redispersible plastic powders suitable for wallpaper paste. See U.S. Pat. No. 4,532,295 issued July 30, 1985 to H. Brabetz et al.
Unmodified and/or derivatized starches are useful as protective colloids in the preparation of aqueous polymer dispersions, e.g., those prepared from styrene, acrylate, methacrylate, acrylonitrile, methacrylonitrile, dienes, vinyl esters including vinyl acetate, allyl esters, and vinyl halides. Suitable starches contain not more than 30% by weight of amylose and include unmodified gel starches, i.e., starches made soluble by boiling in water, and/or hydrolyzed starches (e.g., dextrins).